1. Field of the Invention
The present invention relates to a network system, a node device and a communication method for the network system and, more particularly, to a node device for connecting a plurality of terminal equipments, a network system constituted by a channel multiplex transmission path using a plurality of channels (wavelengths or the like) for connecting a plurality of node devices, and a multihop transmission method, in the node device and the network system, for converting data to be transmitted into a packet, and relaying and transmitting the packet by a node device or devices located on the transmission route between the source terminal equipment and the destination terminal equipment.
The present invention also relates to a terminal equipment connection table generation method for setting packet addresses, and a connection information registration method for registering connection information of the own terminal equipment to the network in another terminal equipment.
2. Related Background Art
In recent years, in order to realize a high-speed network that connects terminal equipments in correspondence with high-speed terminal equipments, various kinds of network systems that use an optical wavelength multiplex transmission path using a plurality of wavelengths have been examined. As one of these network systems, a multihop network system which relays and transmits a packet by a node device or devices located on the transmission route between the source equipment and the destination terminal equipment is known. This system is explained in "WDM-Based Local Lightwave Networks Part II: Multihop Systems", Biswanath Mukherjee, IEEE Network, July (1992), pp. 20-32.
FIG. 1 shows the connection arrangement of node devices 101 to 112 in a first multihop system. Eight rings are constituted by using eight wavelengths .lambda.1 to .lambda.8 in a single optical fiber, and each node device transmits/receives only optical signals of two specific wavelengths indicated by marks .omicron.. FIG. 2 shows the arrangement of the node device. Fixed wavelength receiving means I 201 and II 205 respectively receive optical signals of predetermined wavelengths assigned to each node device. A 3.times.3 exchange SW 202 has three input terminals and three output terminals. The exchange SW 202 receives a total of three data, i.e., the two outputs from the two fixed wavelength receiving means 201 and 205, and transmission data output from a packet processing unit 208 to another node device via a sub transmission path, and outputs these data to one of FIFOs I 203 and II 206, and the packet processing unit 208 connected thereto via the sub transmission path. The FIFOs I 203 and II 206 temporarily store data of optical signals transmitted from fixed wavelength transmitting means I 204 and II 207. The fixed wavelength transmitting means I 204 and II 207 transmit optical signals at fixed wavelengths designated for each node device.
FIG. 3 shows the format of a packet to be transmitted in the first multihop system. Referring to FIG. 3, the packet has an address portion 301 indicating the destination terminal equipment of this packet, and a data portion 302 to be carried by the packet.
FIG. 4 shows the arrangement of the 3.times.3 exchange SW 202. Referring to FIG. 4, each of decoders 401 reads the destination address of an input packet, and outputs, to an SW control unit 402, output designation data for designating one of outputs X, Y, and Z as an output destination of this packet. The SW control unit 402 performs arbitration control on the basis of the output designation data output from the decoders 401, so that packets input from inputs A, B, and C do not collide in a 3.times.3 SW 403, and thereafter, sets connections between the inputs A, B, and C and the outputs X, Y, and Z of the 3.times.3 SW 403. The 3.times.3 SW 403 outputs packets input from the inputs A, B, and C to predetermined ones of the outputs X, Y, and Z under the control of the SW control unit 402.
In the node device of the first multihop system, packets output from three means, i.e., the fixed wavelength receiving means I 201 and II 205 and the packet processing unit 208 are input from the inputs A, B, and C. Each decoder 401 reads the address of the destination terminal equipment of an input packet, one of the fixed wavelength transmitting means I 204 and II 207 as an output destination for transmitting a packet at a predetermined transmission wavelength corresponding to the reading address or the packet processing unit 208 for performing packet reception processing is selected, and the connections between the inputs and outputs of the 3.times.3 SW 403 are set under the control of the SW control unit 402. Then, the packet is output from a desired output destination.
In the network system using the above-mentioned node device, for example, when a packet is to be transmitted from the node device 102 to the node device 109, if the transmission wavelength of the node device 102 is different from the reception wavelength of the node device 109, the node device 105 located therebetween performs a relaying operation for changing the wavelength of the packet and transmitting the packet. More specifically, the node device 102 serving as a source transmits a packet using an optical signal of the wavelength .lambda.3. The optical signal of the wavelength .lambda.3 is received by the fixed wavelength receiving means of the node device 105, and is temporarily stored by the 3.times.3 exchange SW 202 in the FIFO corresponding to the fixed wavelength transmitting means of the wavelength .lambda.1. Then, the packet is transmitted from the fixed wavelength transmitting means as an optical signal of the wavelength .lambda.1. The optical signal of the wavelength .lambda.1 is received by the fixed wavelength receiving means of the node device 109 serving as a destination, and is input to the packet processing unit 208 via the 3.times.3 exchange SW 202. The packet is then subjected to predetermined reception processing in the packet processing unit 208. In this manner, in the node device which relays and transmits a packet, the transmission wavelength is switched to the wavelength corresponding to the destination address 301 decoded by the corresponding decoder 401, and the packet is transmitted at the switched wavelength.
The arrangement of a node device used in a multihop system invented by the present inventors will be described below for the purpose of a reference. FIGS. 5A and 5B show the arrangement of a node device of this example. Referring to FIGS. 5A and 5B, a control section 501 controls the reading operations of buffers I 520 to VIII 527, and also controls the transmission wavelengths of variable wavelength transmission units I 528 to VIII 535. An optical fiber 502 serves as an optical wavelength multiplex transmission path. A divider 503 divides an optical signal transmitted from the optical fiber 502 and outputs the divided optical signal to eight fixed wavelength reception units I 504 to VIII 511. Each of the fixed wavelength reception units I 504 to VIII 511 receives only a packet transmitted as an optical signal of a corresponding one of wavelengths .lambda.1 to .lambda.8. Separation-insertion units I 512 to VIII 519 have a function of separating packets to be transmitted to sub transmission paths I 537 to VIII 544 from packet flows output from the fixed wavelength reception units 504 to 511 and outputting them onto the sub transmission paths I 537 to VIII 544, and a function of inserting packets transmitted from the sub transmission paths I 537 to VIII 544 into the packet flows output from the fixed wavelength reception units 504 to 511. The buffers I 520 to VIII 527 have a function of temporarily storing packets output from the separation-insertion units 512 to 519. Each of the variable wavelength transmission 535 converts a packet output from a corresponding one of the buffers 520 to 527 into an optical signal of a predetermined one of the wavelengths .lambda.1 to .lambda.8 under the control of the control section 501, and outputs the converted signal onto the optical fiber 502 via a wavelength multiplexer 536. These variable wavelength transmission units are controlled so that multiple variable wavelength transmission units do not transmit packets using an identical wavelength. The wavelength multiplexer 536 multiplexes optical signals of the wavelengths .lambda.1 to .lambda.8 output from the eight variable wavelength transmission units 528 to 535, and outputs the multiplexed signal onto the optical fiber 502. The sub transmission paths I 537 to VIII 544 serve as packet transmission paths between the separation-insertion units 512 to 519 and terminal equipments I 545 to VIII 552. The terminal equipments I 545 to VIII 552 are respectively connected to the sub transmission paths I 537 to VIII 544. These terminal equipments receive packets output from the separation-insertion units 512 to 519, generate packets to be transmitted to other terminal equipments, and transmit them to the separation-insertion units 512 to 519 via the sub transmission paths 537 to 544.
Note that the format of a packet in the second multihop system as the example is the same that to be transmitted in the above-mentioned first multihop system.
FIG. 6 shows the arrangement of a network system using the node device of the second multihop system shown in FIGS. 5A and 5B, and exemplifies a case wherein four node devices are connected via optical fibers. Node devices 601 to 604 are equivalent to that shown in FIGS. 5A and 5B, and eight terminal equipments are connected to each node device via eight sub transmission paths. Optical fibers 605 to 608 constitute an optical wavelength multiplex transmission path.
FIG. 7 shows the internal arrangement of each of the separation-insertion units I 512 to VIII 519 used in the node device of the second multihop system. The separation-insertion units I to VIII have the same internal arrangement. Referring to FIG. 7, a decoder I 701 reads a destination address 301 of an input packet and instructs a demultiplexer 702 as to whether or not this packet is to be output to an I/F (Interface) unit 703. The demultiplexer 702 outputs an input packet to the I/F unit 703 or a FIFO II 705 in accordance with an instruction from the decoder I 701. The I/F unit 703 outputs a packet output from the demultiplexer 702 onto the sub transmission path, and outputs a packet input from the sub transmission path to a FIFO I 704. The FIFOs I 704 and II 705 temporarily store input packets, and output the stored packets to a selector I 707 in the input order under the control of an insertion control unit 706. The insertion control unit 706 controls the reading operations of the FIFOs I 704 and II 705, and instructs the selector I 707 of the FIFO to be selected, thereby inserting a packet transmitted from the sub transmission path into a packet flow output from the fixed wavelength reception unit. The selector I 707 selects the FIFO that stores a packet signal to be output in accordance with an instruction from the insertion control unit 706.
FIG. 8 shows the detailed arrangement of each of the buffers I to VIII used in the node device of the second multihop system. Referring to FIG. 8, a decoder II 801 reads an address portion 301 indicating the destination terminal equipment of an input packet, and instructs a writing address counter 802 of the writing start address value of a dual port memory 804 in which the packet is to be written in accordance with the destination of the packet. The writing address counter 802 sequentially outputs address signals of the packet to the dual port memory 804 in accordance with the writing start address value output from the decoder II 801. A reading address counter 803 sequentially outputs reading address signals of a packet to the dual port memory 804 using an offset value output from a buffer control unit in the control section 501 as the reading start address. The dual port memory 804 independently performs the writing and reading operations of the packet data 302. The memory region of the dual port memory 804 is divided in correspondence with the wavelengths to be used upon transmission.
FIG. 9 shows the arrangement of the terminal equipment. Referring to FIG. 9, an I/F (Interface) unit 901 outputs a packet output from a packet processing unit 902 onto a corresponding one of the sub transmission paths 537 to 544, and outputs a packet input from the corresponding sub transmission path to the packet processing unit 902. The packet processing unit 902 obtains the value of an address portion 301 corresponding to the destination terminal equipment by looking up a terminal equipment connection table 903, and writes the obtained value in a predetermined section of a header, i.e., adds the value to data to be transmitted to form a packet. Also, the unit 902 removes the header portion of a received packet input via the I/F unit 901, and performs predetermined reception processing. The terminal equipment connection table 903 has address information of the respective terminal equipments connected to this network system. An input/output unit 904 has an interface function such as a keyboard, a display device, and the like.
In the second multihop system described above, a packet output from the source terminal equipment is inserted into a packet flow output from a corresponding one of the fixed wavelength reception units 504 to 511 by a corresponding one of the separation-insertion units 512 to 519. The address of the destination terminal equipment is read by a corresponding one of the buffers 520 to 527, and the packet is temporarily stored in the memory region corresponding to the reading address. Thereafter, the packet is output from a corresponding one of the variable wavelength transmission units 528 to 535 as an optical signal of a predetermined wavelength, and is relayed by the node devices present before the node device to which the destination terminal equipment is connected. In each node device that performs the relaying operation, the address of the destination node device is read by the decoders in the separation-insertion units 512 to 519 and the buffers 520 to 527, and the packet is then written in a predetermined memory region of the dual port memory 804. The stored packet is transmitted from a corresponding one of the variable wavelength transmission units 528 to 535 as an optical signal of a predetermined wavelength. By repeating the relaying operation, a corresponding one of the variable wavelength transmission units 528 to 535 of the node device immediately before the node device, to which the destination terminal equipment is connected, converts the packet into an optical signal of the wavelength to be received by a corresponding one of the fixed wavelength reception units 504 to 511 for outputting packets to the separation-insertion units 512 to 519 to which the sub transmission path 537 to 544 including the destination are connected. The packet output from the variable wavelength transmission unit is received by the predetermined fixed wavelength reception unit, and is then output from the separation-insertion unit to the sub transmission path. Then, the packet is received by the destination terminal equipment. As described above, in the second multihop system, in the relaying operation of the node device, the address 301 of the destination terminal equipment is read, and the packet is transmitted at the transmission wavelength corresponding to the reading address, thereby routing a packet to a desired terminal equipment of a desired node device.
In the first and second multihop systems, since each decoder has a large hardware scale, as will be described below, each node device becomes expensive.
FIG. 10 shows the arrangement of the decoder used in the 3.times.3 exchange SW in the first multihop system shown in FIG. 4 or in the separation-insertion unit and the buffer in the second multihop system, and exemplifies an arrangement for decoding the addresses of n terminal equipments.
Referring to FIG. 10, a latch 1001 has a function of temporarily storing the destination address portion 301 of an input packet. A decoder management unit (not shown) writes the addresses of n terminal equipments respectively in n memories 1002. Comparators 1003 compare the destination address of the packet temporarily stored in the latch 1001 with the addresses stored in the memories 1002. When the two addresses coincide with each other, each comparator 1003 outputs a coincidence signal to a table address generator 1004. The table address generator 1004 generates a table address for reading out an output designation table 1005. The output designation table 1005 stores desired output designation data. The table address generated by the table address generator 1004 is an address for reading out a table corresponding to the serial number of the comparator 1003 that generated a coincidence signal, and hence, the output designation data of the table corresponding to the destination address of the input packet is read out. Based on this output designation data, the output destination of the packet to be transmitted using a desired transmission wavelength, is determined.
As described above, in the decoder with the above arrangement, the destination address of an input packet is compared with the addresses of all the terminal equipments connected to the network system, and output designation data is read out from the output designation table on the basis of the matching address of the terminal equipment as a result of comparison. For this reason, the number of required pairs of memories and comparators must be equal to or larger than the number of terminal equipments connected to the network system, and the number of table data stored in the output designation table must also be equal to or larger than the number of terminal equipments. Furthermore, the table address generator requires a longer time for generating table addresses as the number of input coincidence signals increases.
Therefore, the decoder with the above arrangement requires a larger hardware scale and higher cost and becomes difficult to attain high-speed address decoding as the number of terminal equipments connected to the network system increases, thus hampering a high-speed operation of the network system.
The present invention has been made in consideration of the problems of the prior art and the example, and has as its object to provide a low-cost node device by preventing an increase in hardware scale of the node device by a node device and a communication method which allow to simplify decoders in the node device, and to realize a high-speed operation of a network system.